The present invention relates to a printing method and a printing press, and particularly to a printing method of developing an on-press type printing plate precursor mounted on a printing press with emulsion ink and carrying out printing, and a printing press employing the method.
Recently, a printing press equipped with an image forming means represented by an infrared laser irradiation device, a so-called DI printing press, has been focused on as a system for prompt delivery of prints and reduction of printing cost. As the DI printing press, there are a printing press employing dampening water and a waterless type printing press employing no dampening water, as in an ordinary printing press.
The waterless type DI printing press has no device for supplying dampening water, and even if the press is installed with an image forming system, it can be structured very compactly. For example, there are provided printing presses such as Quickmaster-46-DI produced by Heidelberg Co., Ltd. and 3404DI produced by Ryobi Co., Ltd., which can be installed in a reduced space, and can be applied in an office environment.
The waterless type printing press does not require the delicate control of dampening water supply amount nor any special operation skill, which is one of the elements suitable for an office environment.
FIG. 1 shows the fundamental structure of Quickmaster-46-DI produced by Heidelberg Co., Ltd. This printing press has four sets each including a blanket cylinder 2, a plate cylinder 1, an ink supply system 4, and an infrared laser exposure system 5 in a satellite state around an impression cylinder 3 having a diameter 4 times greater than that of the plate cylinder 1.
FIG. 2 shows a sectional view of a plate cylinder 1, which illustrates in detail the interior of the plate cylinder 1. That is, the plate cylinder 1 has, within the cylinder, a supply spool 1b and an uptake spool 1c, and has a construction in which a printing plate precursor 9 is stored in the roll form on supply spool 1b within the cylinder, unrolled, withdrawn through an opening 1a, brought onto the outer surface of the cylinder and wrapped around the cylinder, reintroduced through opening 1a into the cylinder, and received by uptake spool 1c within the cylinder.
Fixation of a printing plate precursor on the plate cylinder can be carried out, for example, by locking either one of the supply spool or the uptake spool not to rotate, applying a rotational torque in the rotational direction to the other spool to apply a certain tension to the plate precursor, and then locking it. Further, the interior of the plate cylinder as disclosed in Japanese Patent O.P.I. Publication No. 7-101044 is also usable.
Further, as in the printing press disclosed in Japanese Patent O.P.I. Publication Nos. 11-28802, which has a plate cylinder composed of two cylinders, one being an outer hollow cylinder having orifices and the other an inner cylinder, fixation of a plate precursor on the plate cylinder can be carried out by mounting the plate precursor on the outer, hollow cylinder, and then sucking air through the orifices from beneath the plate mounted on the outer cylinder.
The printing method comprises the steps of withdrawing a printing plate precursor 9 stored in the roll form (resin material) within the plate cylinder 1, bringing it onto the outer surface of the plate cylinder 1 to wrap the cylinder, imagewise exposing the precursor employing an infrared laser exposure system 5 to ablate the exposed portions of the precursor, cleaning the surface of the exposed precursor through a cleaning system 6 to remove the ablation residue to form an image, and subsequently supply ink onto the surface of the resulting precursor through an ink supply system 4, whereby printing is carried out. A water supply is not needed, since a waterless printing plate precursor is used, and the printing press has no water supply system, since a waterless printing plate precursor is exclusively used.
Printing paper is fed to an impression cylinder 3 from a printing paper feeding section 7. Four different color inks transferred from four plate cylinders 1 to four blanket cylinders 2 are sequentially transferred to the printing paper to obtain four-color prints, which is subsequently supplied to a delivery section 8.
As described above, a waterless printing plate precursor makes it possible to use a compact printing press relative to the size of the paper sheet to be printed. The waterless printing plate precursor, which is presently supplied for a DI printing press, is an ablation type waterless printing plate precursor, and requires cleaning of the printing plate precursor surface after laser exposure as described above to form an image. This cleaning step increases the set-up time for printing, which is one factor of the cost increase. Further, use of a cleaning solution and non-woven fabric for cleaning also adds to the cost increase.
In contrast, as a printing plate precursor used in the DI printing press employing dampening water, a so-called xe2x80x9cprocessless CTP materialxe2x80x9d, there is a printing plate precursor disclosed in, for example, U.S. Pat. Nos. 2,938,397 and 2,938,398, which comprises a hydrophilic support having thereon an imaging layer containing heat-fusible hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder. In this precursor, a so-called xe2x80x9con press developmentxe2x80x9d is required, which comprises the steps of mounting the precursor on a plate cylinder of a printing press, exposing the precursor employing a laser, and supplying dampening water and ink onto the surface of the exposed precursor while rotating the plate cylinder to remove unexposed portions of the imaging layer. As compared with the waterless printing plate precursor as described above, this printing plate precursor does not require an exclusive plate surface cleaning system nor processing materials thereof, reducing the running cost. However, the printing plate precursor has the problem in that the set-up time for printing resulting from on press development increases.
Recently, there has been developed a printing plate precursor which starts printing without cleaning the printing plate surface nor carrying out on press development in the same manner as in a conventional PS plate, and exhibits the same rise in printing as the PS plate, for example, the printing plate precursor as disclosed in Japanese Patent Application No. 11-358969. Application of such a printing plate precursor to a DI printing press requires no exclusive printing plate surface cleaning system and makes it possible to markedly reduce a set-up time for printing, resulting in the possibility of reducing the running cost.
However, at present, even if such a printing plate precursor is applied, the DI printing press is considered to need the same continuous water supply system as that of a printing press used in the PS plate, and has a construction in which an image forming system is installed in a general unit type printing press (carrying out one color printing per one unit) (for example, Speedmaster 74-DI series produced by Heiderberg Co. Ltd.), which requires a large establishment area relative to the printing sheet size.
Further, since the printing plate precursor employs dampening water in printing, a printing skill is required.
There is disclosed a printing method in U.S. Pat. No. 6,095,048, which comprises the step of (b) imagewise exposing an ablation type printing plate precursor (a) employing water which has an outermost layer containing polyvinyl alcohol capable of being removed by a non-aqueous single fluid ink, and (c) removing the outermost layer by carrying out printing employing the non-aqueous single fluid ink. Use of polyvinyl alcohol in a protective layer results in various problems that background contaminations are likely to be produced at the initial printing stage and staining is likely to be produced at portions of the printing plate precursor where fingers touched, even in the conventional printing methods. In this case, a counter measure such as use of dampening water containing alcohol is required, but an optimum combination of the structure or materials used of the printing plate precursor with the single fluid ink has not still been developed.
An object of the present invention is to provide a printing method employing a printing plate precursor employing dampening water which provides reduced running cost, and does not require a high degree of skill, and to provide a printing press for a printing plate precursor employing dampening water which is capable of being small-sized, reduces running cost, and does not require a high degree of skill.
The above object has been attained by one of the following constitutions:
1. A method of printing an image with a printing plate prepared from a printing plate precursor, which comprises a support having thereon an image forming layer A containing a water-soluble material, the method comprising the steps of:
(a) imagewise exposing the layer A of the printing plate precursor so as to form an unexposed portion and an exposed portion;
(b) supplying an emulsion ink containing an oil-based ink and water onto the layer A so that the unexposed portion is removed from the layer A so as to form a non image portion and the exposed portion remains in the layer A so as to form an image portion to give the printing plate, wherein the image portion is lyophilic and the non image portion is hydrophilic; and
(c) printing the image on the printing plate to an image receiving material while further supplying the emulsion ink.
2. The method of item 1, wherein the water-soluble material in the layer A is a saccharide.
3. The method of item 1, wherein the printing plate precursor further comprises a hydrophilic layer B between the support and the layer A, wherein the layer A further comprises heat-fusible particles or thermoplastic particles.
4. The method of item 3, wherein the water-soluble material in the layer A is an oligosaccharide.
5. The method of item 3, wherein the hydrophilic layer B is a porous layer.
6. The method of item 3, wherein the hydrophilic layer B further comprises a light-heat conversion material.
7. The method of item 1, wherein the printing plate precursor further comprises a layer C which is capable of being ablated and a hydrophilic layer B on the support in that order, the layer A being located on the layer B.
8. The method of item 7, wherein the water-soluble material in the layer A is a polysaccharide.
9. The method of item 1, wherein the printing is carried out without supplying water on the surface of the printing plate during printing.
10. The method of item 1, wherein water is supplied on the surface of the printing plate precursor prior to supplying the emulsion ink on the surface of the printing plate precursor.
11. The method of item 10, wherein water is supplied with a water spraying device on the surface of the printing plate precursor.
12. The method of item 11, wherein an amount of water W (g/m2) supplied on the surface of the printing plate precursor and a coating coverage Q (g/m2) of the layer A satisfy the following formula,
0.1xe2x89xa6W/Qxe2x89xa650. 
13. The method of item 1, wherein the step (a) is carried out after the printing plate precursor is mounted on a plate cylinder of a printing press.
14. The method of item 1, wherein an infrared laser is employed for imagewise exposing the printing plate precursor.
Examples of printing presses for the above-mentioned methods are as follows.
(i) a printing press comprising an exposure system employing an infrared laser capable of forming an image on a printing plate precursor mounted on the plate cylinder and comprising no water supply system for continuously supplying water onto the surface of the printing plate precursor during printing.
(ii) a printing press comprising an exposure system employing an infrared laser capable of forming an image on a printing plate precursor mounted on the plate cylinder and a water supply system for supplying water onto the surface of the printing plate precursor so that water does not directly contact ink.
(iii) the printing press of item (ii), comprising a water supply system which brings a water supply roller into contact with the surface of the printing plate precursor while rotating the plate cylinder to supply water onto the printing plate precursor surface, and then separates the water supply roller from the printing plate precursor surface before carrying out printing by bringing an ink supply roller into contact with the surface of the printing plate precursor.
(iv) the printing press of item (ii), wherein the water supply system is a water spraying device which is capable of spraying water onto the surface of the printing plate precursor.